Systems for beaconing and radio position determination



Dec. 13, 1955 P, GAUDlLLERE 2,727,231

SYSTEMS FOR BEACONING AND RADIO POSITION DETERMINATION Filed Aug. 6,1952 4 Sheets-Sheet 1 Freq/020g emu/t/,o//cat/bn @zufall-gv 3 pf2/*re@aad/Wert /NVENTOR @Y @gf-JW Dec, 13, 1955 P. GAUDILLERE 2,727,231

SYSTEMS FOR BEACONING AND RADIO POSITION DETERMINATION Filed Aug. 6,1952 4 Sheets-Sheet 2 TL- K 39 Dec. 13, 1955 P. GAUDILLERE 2,727,231

SYSTEMS FOR BEACONING AND RADIO POSITION DETERMINATION Filed Aug. 6,1952 4 Sheets-Sheet 3 Detector fransmizer Generator l R 17%[0 r f7 T/ Bl* P-g Msg#- M FB M k l @usage 20/ Selsgfz Selig/fz Sigan Motor Receiverjeceivef (Y 69 (Y 66 Y f /D/'erre Good/Were /NVEN TOR By we ggZMATTORNEYS Dec. 13, 1955 P. GAUDILLERE 2,727,231

SYSTEMS FOR BEACONING AND RADIO POSITION DETERMINATION Filed Aug. 6.1952 4 Sheets-Shea?l 4 /D/'e fr e Gand/Were /V VE/V TO l? ATTORNEYSUnited States Patent Oiice j 2,727,231 Patented Dec. 13, 1955 SYSTEMSFOR BEACNING AND RADI POSITION DETERMINATION vPierre Gaudillere,Neuilly-sur-Seine, France Application August 6, 1952, Serial No. 302,973Claims priority, application France August 16, 1951 20 Claims. (Cl.343-105) Numerous types of systems exist that permit the beaconing ofspace and the identification of the location of a mobile or stationarypoint.

Among these systems are those that enable the operator to determine hisposition in a given area (hereinafter termed subjective positiondetermination) and those that permit the determination of the positionof particular points in a given area (hereinafter termed objectiveposition determination).

An object of the invention is to provide a system permitting both asubjective and objective position determination of radio receiversrelative to radio transmitters.

Another object is to provide such a system which operates by providingin space a mobile line that is the locus of points at which the phasesof signals emitted by two transmitters are equal.

A further object is to provide means whereby this position determinationmay be effected by utilizing modulated carrier waves, this modulationbeing of any kind.

A still further object is to provide means whereby it is possible tocommunicate from a controlling point to any selected point in a givenarea.

This invention is equally adaptable for the determination of theposition of fixed or mobile points and is of particular use in thesubjective or objective position determination of mobile objectstravelling at high velocity and more specifically the subjective andobjective position determination of aircraft.

In accordance with the invention, two transmitters are positioned at thetwo ends of a straight line forming preferably the bisecting line of thearea in which position information is desired. Each transmitter emits asignal, the frequencies of these signals being diferent and very closeto each other and subject to certain conditions hereinafter set forth. g

Under these conditions, the locus of the points where the signalsrespectively emitted by the two abovementioned transmitters are in phaseforms a substantially hyperbolic line which moves regularly from onetransmitter to the other and thereby sweeps the area between these twotransmitters. it is evident that if the time elapsed between the passingof the mobile line, termed isophase line, through a point of knownposition and its passing through the point whose position is to bedetermined could be measured, a first position indication of the pointof unknown position would be obtained. It would suftice to emit twosignals from two other transmitters whose connecting line is for exampleperpendicular to the connecting line between the first mentionedtransmitters, to obtain a second position indication similar to theiii-st and thence by intersection finally identify the location of thereceiving point of unknown position.

The invention consists, then, in a system comprising at least one pairof transmitters, the transmitters of each pair being respectivelydisposed at the two ends of a straight line passing through the area inwhich the position information is desired, each transmitter of each pairbeing adapted to emit a signal, and the frequencies of these two signalsbeing different and Very near one another and so chosen that thevelocity of propagationof the waves divided by the sum of the twofrequencies is greater than the distance that lies between these twotransmitters, and said system further comprising means for measuring thetime elapsed, termed time lag, between the reception at the point whoseposition is to be determined of a signal emitted by a xed transmitter atthe moment when the isophase line passes through a known positionreference point arbitrarily selected, and the passage through the pointof unknown position of said curve that is the locus of the points atwhich the two signals emitted by the two said transmitters are in phase.

Advantageously, the passage of this curve through this known positionreference point is detected with the aid of a receiver termed monitorreceiver which is situated at this point and emits a signal S which willbe termed initial signal at the moment the curve or line in questionpasses through this point. Conversely, such a signal S could be emittedperiodically and the signals of the transmitters A and B could be soregulated that the mobile line pass through the reference point at theinstant each signal S is emitted.

The invention will be better understood and other features andadvantages will appear from the ensuing description with reference tothe accompanying drawing, in which: j

Fig. l diagrammatically illustrates the area within which the positiondetermining operations are performed.

Figs. 2 and 3 illustrate two examples of the frequency locking systems.

Figs. 4, 5 and 6 illustrate three examples of devices that detect thepassing of the isophase line.

Fig. 7 diagrammatically illustrates the Way in which the detectingdevice-represented in Fig. 6 operates.

Fig. 8 diagrammatically illustrates an exploded view of a stroboseopicdevice for measuring the time lag.

Fig. 9 diagrammatically illustrates an electro-mechanical device formeasuring the time lag.

Fig. l0 illustrates a set of transmitting systems that effect theobjective and subjective position determination.

Fig. l1 illustrates the system at the point whose position is to bedetermined.

Fig. 12 illustrates the receiving system at the control post whicheffects the objective position determination.

Fig. 13 diagrammatically illustrates a part of a hyperbolic networkcreated by two transmitters utilizing pulse modulation.

Fig. 14 diagrammatically illustrates a signal filtering and countingdevice.

15 diagrammatically illustrates a part of a monitor receiver.

Fig. 16 diagrammatically illustrates a coincidence detector.

Fig. 17 diagrammatically illustrates a receiver employed in thesubjective position determination by means of pulse modulated waves.

According to the illustrated embodiment, two transmitters A and B(Fig. 1) spaced apart by a distance d emit respectively signals whosefrequencies p and q are vvery close to one another. It will be supposedfor instance that p is slightly greater than q. If the amplitudes ofthese signals vary sinusoidally, the amplitudes are proportional to:

(sin (Zn-pt-I-qal) and sin (21rqt-l-tp2) where 9:1 and pz are the phasesat the time origin.

At any point M where AM=r1 and BM =r2, the amplitude of the receivedsignals are proportional to where c is the velocity of propagation ofthe waves.

At the instant when the phases of these two signals are equal,V there isobtained:

where K is a whole number.

At ay point M determined by the magnitudes r1 and r2, the. phases of thetwo signals p` and q are equal at the instant t defined by thisequation. Inthis equation onlyV r1 and r2 are variable. In consequenceat every point at which. pri-qrz has the same value, the phases of thesignals having the respective frequencies p and q arel simultaneouslyequal. These points form aV curve termed Descartes oval expressed by theequation pr1-qrz=U, where U is a constant. The shape of this curve issubstantially that of a branch of a hyperbola having foci A and B if themagnitudes of p and q are very close to one another.

This curve moves with a continuous motion from A to B. On the axis AB,for which r2=d-r1:

cui-q) The speed of the movement from A to B is dfi P q =f-=c.-- d# 11+@thisv speedl beingclose to c 1l-q :aan (p-I-q) sin 6' sin 6 when p and qare close.

It is seen` then, that theY speed of movement of the isophase line maybe regulated at will bythe selection of the frequencies, p and q. Inparticular they may be rendered much less than the velocity c of radiowaves, while remaining much more than the velocity of the fastestaircraft.

Thus,l extensive areas may be swept within the period of the order of asecond. This provides data on the positions of mobile objects at a ratesucientlyy rapid for the indication of the position obtained to beconsidered as practically continuous.

Taking the equation:

@(peq) it is easily seen, since K' is a whole number, that. two.successive passages of the isophase line through any point M occurfortwo values of K that diler by one, i. e. at two instants separated byan interval of time:

71:; 29"9 T will be termed the sweep period.

It is obvious that to be able toemploytisophase lines 4 for positiondetermination it is very desirable that there exist at any given instantonly one isophase line at the most in the considered area. For this, itis necessary and sufficient that the distance d between the transmittersbe less than that traveled through by the isophase line on the axis ABduring the period T.

It is, then, necessary that:

is the condition of non-ambiguity and it xes the maximum permissibleseparation of the transmitters as a function of the frequencies p and q,so that the data provided are not ambiguous.

If, this condition is satised, it is possible to alirm that a receiverthat detects at a given instant the passage of the isophase line isnecessarily on a curve pr1-qr2=U, the magnitude U being determined bythe. instant of passing and, further, that the position of this isophasecurve at the. moment when it passes through the receiver is denedwithout ambiguity since there is only one isophase curve at, a timebetween the transmitters.

The following points will be examined in turn:

(a) The nature of the system- (general considerations).

(b) Subjective position determination (detection of the passage of theisophase curve-measurement of the time lag).

(c) Objective position determination.

(d) Selective connections with the points to be located.

THEl NATURE OF THE. SYSTEMl General considerations To determine theposition of a point M, there is measured the time that elapses betweenthe reception at the point M of a signal S (hereinafter termed initialsignal) emitted by a point of reference R at the moment when theisophase line. I (Fig. l) passes through. this point and the moment whenthe isophase line passes through, the point M. M

To this end, a special receiver (hereinafter termed monitorreceiver) isemployed which. indicates the passage of the. isophase line and provokesthe emission of an initial signal S at the instant to when the isophaseline passes through R.

When subjective position determination is considered (Figs. 4, 5 and l0)there will be described the various devices utilized for indicating thepassage of the isophase :line-and emitting a signal at this instant.

The point R may coincide with the point at which transmitter A islocated. Advantageously the point R is placed at a distance from A thatis just sucient to permit it to receive signalsA other than thoseemitted by A. Under thesev conditions the signal S could be emitted bythe transmitter at A. This is important for reasons hereinafterexplained. This, in fact, permits recourse to another method for theproduction of the initial signal S as will beunderstood later.

which may be expressed:

The points at which the time lag is the same are situated on thebranches of the hyperbolae having as foci A and B defined by theequation r1-r2=constant, and which will be termed position hyperbolae.Thus there is obtained a first positionl hyperbolae network which willbe termed network AB.

It suices to repeat the operation with two other transmitters A' and Bto define another isophase line II (Fig. 1). In this way anotherposition hyperbolae network will be obtained.

The intersection of theposition hyperbola of the network AB passingthrough the point M with the position hyperbola of the network ABpassing through this point permits the determination of the position ofthe point M. Advantageously the transmitters A and B' are placed at theends of a straight line that is the perpendicular bisector of thestraight line AB.

In order to distinguish position determination by means of thetransmitters AB from determination by means of transmitters AB,reference will be made hereinafter to position determination in networkAB and position determination in network AB'.

For this method of position determination to be practicable, it isnecessary that the magnitude vo be of the order of some hundreds ofkilometres per second and that of T of the order of a second. Theselection of vo and T is sufficient to determine the frequencies p and qsince:

As seen, the frequencies p and q that are practicable belong to therange of audio-frequencies. To transmit them it would be advantageous toemit from transmitters A and B carrier waves FA and FB which aremodulated by oscillations having frequencies of p and q. The frequenciesof these carrier waves are selected solely as a function of theconditions of propagation and allocation of the frequencies'. Thecarrier wave frequencies of A and B must, moreover, be distinct, for themodulation frequencies of p and q are too close to one another for theirseparation by low-frequency filters.

Further, it will be necessary to use for the transmitters A' and B twoother different frequencies FA' and FB' which may be modulated with theaid of the same frequencies p and q. In practice the frequencies of thesignals emitted at A and at B and at A' and at B' will be separated bysome kilocycles.

The modulation of the carrier wav'es may be eected in accordance withany of the known methods. For instance, use may be made of:

(a) Sinusoidal modulation of the carrier wave amplitude in accordancewith the above example.

(b) Sinusoidal modulation of the frequency of the .carrier wave.

(c) Pulse modulation. A

It is evident that in the last case there is strictly speaking noquestion of measuring the coincidence of phases since the waves offrequencies p and q are replaced by pulses. Instead of measuring phasecoincidences, the coincidences of the two pulses are detected, eachpulse being emitted from one of the transmitters; this defines distincthyperbolae moving in jumps from A to B and corresponding to successivemagnitudes of time lag. The space is divided by these hyperbolae intochannels inside of which is the mobile object. In this case thedetermination of position will be effected by channels as will besubsequently described.

The specific case of transmitters modulated in amplitude by frequenciesp and q will be considered hereinafter.

Locking of the frequencies The accuracy of position determinationdepends essentially on the exact knowledge of the velocity vu and theaccuracy with which the time lag -r is measured.

The equation C12-q p-l-q shows that if a relative error in the values ofp and q is E, under the worst conditions there may be a relative errorin v0 equal to P could then be maintained constant to the nearestmillionth. Similarly with the velocity l-P U- 61+!) Very many methodsexist for the locking of the frequencies p and q.

The frequencies may, for example, be locked by stepping down from anoscillation having a frequency that is a multiple of p and q, or bymultiplication stepping up from an oscillation having a frequency thatis submultiple of p and q.

If, for example, p=(K-}l) (p-q) and q=K (p-q) where K and K+1 are twoconsecutive whole numbers,

the frequency of the smallest common harmonic of p and q is: K(K{1)(p-q) and the frequency of the smallest sub-harmonic: p-q. The onlycondition for this is that the frequencies p and q be commensurable withtheir difference p-q i. e. exact multiples of p-q. Moreover, it isadvantageous to have p-q=l corresponding to a sweep period of onesecond.

By way of illustration, two devices (Figs. 2 and 3) permitting thislocking, will now be described.

The first device (Fig. 2) makes use of chains of frequencymultiplication or division.

A receiver 1 is employed in the proximity of the point A. It will beunderstood later that it coincides with the monitor receiver R thatdetects the signal of frequency q emitted by B and this signal isapplied to a frequency multiplication chain 2 which delivers theharmonic of class K-l-l. This new oscillation has for atrae-.2811..

frequency (K4-l) q=K (K-l-l) (p--q)I i. e. the: smallest harmonic commonthev frequencies p and q. It is. applied to a frequency demultiplicationchain 3 whichdelivers. the subharmonic oscillation of class K. The.frequency of this oscillation is It is employed for modulating thetransmitter A.

For aiding the construction of the multiplication or demultiplicationchains, itis well to select for K and K|l whole consecutive numbers thatare reduceable to prime factors as low as possible, for example:

For purposes of locking the frequencies, synchronization signals emittedby the transmitter A for example may be utilized (see Fig. 3).

The transmitter A emits, for instanceA by means of a pendulum,synchronization pulses of frequency p'q. say for example 385c-384c=l,which is the grestest subharmonic common to the frequencies p and q.These pulses are utilized at 4a for vibrating a tuning fork 5. Further,the carrier wave FA emitted by thetransmitter A is modulated by thefrequency p-ql and by the frequency p with the aid of modulators 4b and5a. The wave FA thus modulated is received by a. special receiver 6 atthe transmitting station B. The pulses p-q are detected at 7 andutilized to vibrate at 8 a tuning fork 9 of frequency K(p-q)=q which isemployed toy modulate at 10 the wave FB emitted by the transmitter B.

The pulses p-q are, for example, produced by a pendulum beating thesecond; the tuning forks utilized are-l in Invar metal enclosed inthermostatic containers and tuned respectively to frequencies p and q.The very slight errors that could occur inv these tunings are correctedby pulses produced in electromagnets, thereby insuring thesynchronization of the oscillations of the tuning forks.

It will be understood of course that any otherA appropriate device couldbe utilized in place of the pendulum 4 and the tuning forks 5 and 9.Thus a modification of this solution would be to replace the, tuningforks. by chains of oscillating circuits ensuring the multiplication ofthe reference oscillation by the factors KA and K+1, for exampleObviously any other frequency locking system may be utilized instead ofthose described and illustrated in Figs. 2 and 3. For instance,synchronous motors could be employed fed by the same network or phonicwheels actuated by a reference oscillation (such as the standard signalsemitted by the oieial transmitters), and driving alternators throughsuitably calculated gear trains.

Once the problem of the locking of the frequencies is solved, theisophase lines created with the ai'd of signals of frequency p and q maybe quite safely utilized both for subjective position determination` andobjective position determination.

The subjective position determination comprises:

(a) Detecting the passing of the isophase line.

(b) Measuring the time lag.

The objective position determination comprises causing the production atthe object of unknown position by the passage of the isophase line, of asignal, that permits' a control post to determine the position of' this.object..

SUBJECTIVE POSITION DETERMINATION Detection of the passing of theisophase line The receiver at point M (Fig. 1) which seeks to deter--mine its own position, for example the receiver onboard an aircraft,comprises two high frequency channels re- 8 spectivelytuned. toy the,carrier wavesV of the transmitters A and B. These channels deliver:afterv detection the. two signals of frequencies p and q whose phaseshave to be compared.

Several methods of phase comparison may be envisaged. Three; of Ithesemethods will bev described by way of exampley (Figs: 4 5 and 6.).

Firstly, a simple phasefmeter: (Fig. 4) may be utilized.

The modulated signals- Fn and, FB,- receivedby an anterma pass: throughan. amplifierv 11 and then through two filters 12 and 13 which separatethem. Two' detectors 14. and 15detect thezsignalsof frequency py and q..The current having; one ofi-these frequencies, the frequency p forexample', is applied. with ther usual dephasing to the windings of aphase meter 16 whereas: a current; of frequency' q is applied tol therotor winding 17 of this phase meter.

The pointer 18 of thef phase meter 16 rotates', then,

with a frequency equal'- to p-q, say for example onerotati'on per secondin the casezwhert p=385 andf q=384. When the pointer 18. passeszthroughtheposition at which the difference of phase between currents. havingrespective frequencies ofA p. and q: isanilf, it encounters a. contact19 and.' this Contact delivers a pulse that constitutes the signal ofthe. passage of the isophase line through the pointM.,

According to a particularly advantageous modification (Fig. 5:), thephase meter 16: could bey replacedl by two selsyns. 20/ and: 211.. Therotor 22V of theselsyn 20 is locked and' is fed by' they currentoffrequency p` from the detector 1-4.. The windings 23 and 25. of thetwo selsyns 20 and 2:1? are. connected inseries phase by phase. Therotor 2S of the selsyn 21 is fed by the current of frequency q from thedetector 15. Under these conditions,

lthe rotor 25 rotates at the frequency p--q which is the frequency ofthe sweeping of the isophase lines.

The pointer 26 is driven by the rotor 25 and rotates before a dial 27.It provokes an emission of a signal at the moment when the isophasekline passes through the point M, i. e. when the dephasing between thecurrents having respective frequencies p and q is nil, as in the caseillustrated in Fig. 4. l

Of course any other phase' meter'may be utilized, provided it allows theaccurate detection of the instant when the phase difference is nillAsran example off isophase line detecting systems not employing a phasemete-r, a systemmaking use of beatA positive alternations 30 amplifiedat 31` are squared at 32 and derived. at 33r thereby'providing pulses341 off fre- .quency p-qwhich, correspond with theinstants when21rpt|qp1=21rpt|q 2; i. e. with the passingl of the isophaseline.

. Measurement tof time lag It; will be recalled that time lag is theterm given to .the time that elapses between the reception ofthei'nitial signal S at a point M whose position is to be determined` andthe passing through this point of the isophase line.-

It has been indicated that the emission of the signal S by thetransmitter A (or transmitter B) may be provoked by the detectioneffected with the aid of a monitor receiver, of the passing of theisophase line through a point R arbitrarily chosen and advantageouslysituatedin proximity to the transmitter A (or transmitter B). "Thissignal S is therefore emitted for a Xed time lag TR at the point R. y

The emission of this signal is effected by any known method, for examplethe method employed in the emission of standard frequency signals, andcomprises modulating a carrier wave (which may be that from transmitterA or transmitter B) by means of a particular frequency fo (which is as arule diierent from the `frequencies p and q) and varying the Ymodulatedsignal in such manner as to allow through only a few alternations foreach signal S to emit.

The receiver includes a low frequency filter which is tuned to thefrequency fn and thus gives a pip at the reception of each signal S.

It will be understood that under these conditions, the signal S could bedirectly transmitted from the point A instead of provoking its emissionby the passage of the isophase line at the point R, by giving thissignal the frequency of the sweeping eifected by the isophase line andusing it as the initial signal with'the only condition that the phase ofthe signal of frequency p or that of signal q is so regulated that thetime lag at thepoint R always conserves the fixed value TR mentionedabove.

Under these conditions the time lag measured at a given point M is thesame whatever be the method of emitting the initial signal S. y

Very many kinds of time lag measuring devices may be employed. The timelags to measure are of the order of a second and must be determined tothe nearest 1/1000, which renders fairly delicate the employment of anindependent time measuring device at the point whose position is to bedetermined, for example on board the mobile object. It is preferable toeffect these measurements with the aid of apparatuses locked to thefrequencies p and q and which therefore provide a time basis common toall the receivers of the area.

Some examples of time measuring devices will be described, but it isobvious that any other device may be employed.

Stroboscopic indicator (Fg.'8)

A simple solution consists in utilizing for measuring the time lag thephase meters (Figs. 4 and 5) utilized for the detection of the passingof the isophase line.

The shaft 34 of such a phase meter illustrated at 35 (Fig. 8) drives anopaque disc 36 provided with a radial slit 37. This disc rotates betweenone or several neon tubes 38 and a translucid graduated dial 39 coatedwith a phosphorescent coating 40 whose luminous remanence is of theorder of seconds, i. e. substantially equal to the period of sweeping Tof the isophase line. When the phase meter 35 rotates, the slit 37passes through the zero graduation at the moment when the phase shiftbetween the currents of frequency p and q is nil, i. e. at the moment ofthe passing of the isophase line. Furthermore, itis arranged that thereception of the signal S provokes the lighting up of the neon tube ortubes 38. Under these conditions, the luminous line that appears on thedial indicates theV graduation corresponding to the time lag.

The utilization of the phase meter having two selsyns (Fig. isparticularly recommendedin the case of the stroboscopic device justdescribed. Since the precision of the positioning of a selsyn is of theorder of A of a degree, an accuracy is obtained that is greater thanKom.

"" signal lL termed hereinafter POSOU Signal at the moment i means of agearing and in this way aid the reading. The

graduation is then read as on the dial of a watch especially if n: 12and if the selsyn rotates in an anticlockwise direction.

i Electro-mechanical indicator (Fig. 9)

It is very useful to replace the purely visual signal provided by thestroboscopic indicator of Fig. 8 by the movement of a mechanical member.In this way the amplitude of this movement may be read on a suitabledial and the moved mechanical member may be utilized as a drivingmember, for instance for controlling a delay line, as will behereinafter explained.

The devices having two selsyns above described (Fig. 5) enable aparticularly useful electromechanical indicator to be constructed (Fig.9).

The rotor 22 of the selsyn 20 fed by the current of frequency p, whichwas keyed in the device illustrated in Fig. 5, is in the indicator ofFig. 9 driven by a motor 44.

The rotor 25 of the selsyn 21 rotates at the speed (p--q) revolutionsper second, as in the example in Fig. 5, and drives a brush 45 connectedto a source 46 of direct current. This brush rubs on two collectors 47and 48 each of which forms half a cylinder and is disposed so that theircommon generatrix corresponds to the position of no phase shift betweensignals having frequencies p and q.

The two semi-cylinders 47 and 48 are connected respectively to one ofthe grids of pentodes 49 and 50. These pentodes are thus blockedalternately during intervals of time of The initialsignal S is fed tothe other grid of each of these two pentodes, and the pentode which isunblocked at the moment this signal is received delivers a current thattends to rotate the motor 44. This rotation occurs in one direction whenthe pentode 49 is operative and in the opposite direction when thepentode 50 is operative. The motor 44 drives the rotor 22. It stops ifthe signal S is received at the instant when the brush passes throughthe point of no phase shift that corresponds to the gap that separatesthe two semi-cylinders 47 and 48. This motor drives moreover a pointer51 moving across a dial, or` preferably two geared-down pointers whoseindications are, read' as the time on a watch. The stopping of the motorcorresponds tothe instant when the rotor 22 has been so-displaced thatthe reception of the signal S andI the passing of the brush 45 at thepoint of no phase shift coincide in time.

` Electronic indicator 'A very` accurate method of measuring the timelag comprises emitting, for example by transmitters A and B,synchronization pulses the frequency of which is advantageously lockedwith that of the signal S (the frequency p could, for instance, beutilized to this end), thereafter computing with the aid of anelectronic computer the number of these pulses received at the point Mwhose position is to be determined between the reception of the initialsignal S and the moment when the isophase line passes therethrough.

Many other methods of measuring the time lag may be envisaged and thoseherein described are given of course only by way of example. l

OBJECTIVE POSITION DETERMINATION Objection position determinationcomprises causing the point M of unknown position (which may be forexample on board a moving object such as an aircraft) to emit a menantwheny the isophase line passesi through this point, recev ing this'.signal Lv and deriving therefrom the position` of. thepoint M.

Thus the signal of. thel different points: of unknown'posie tion.dispersed over the surveyed area are emitted at. differ-v ent instants.and a. single wave length( may' be utilized for the entire area.

The signal L emitted by the point M at the moment4 of the passing of theisophase. line. could be received at a control post surveying the areaon the grid of'a cathode tube. the. sweeping of whichv would be.controlled by the initial signal- S and would have, then, thesamefrequency' as that of the sweeping effected: by the. isophase. line.

Under these conditionsthe. luminous. spot would occupy' at each instanton: the screen ofthe cathode tube. azposie tion which. would. correspondto the positiony of the point M in the network AB (Fig. Il, thedistance. AB being" represented on the screen. by the total traveleffected. by the spot.

It would suffice to utilize a second cathode. tube forthe network A'B.'(Fig. l) for determiningI the. position; of the emission. point M in:this latter network. Thus; for example by projection. on a third screenthere. could be obtained by intersection the position of the point Mi ontwo coordinatesone along the. axis ABR andi the other along theaXisAfBl.

It is, however,v much morepreferable:toreplace the two cathode tubes.by` a single television. tube and proceed as follows.

Signals of frequency n.s,. i.. e.. having a frequency thatv is amultiple of the frequency s of the initial signals; are. emitted'. The.frequency n.sA is lockedf with the. frequency s. Hence, the'I areasurveyed is` divided into nl. channels delimited by what will be. termedhyperbolae of coincfdence along which these signals of frequency n s,emit-tedl in the form of pulses or transformed into pulses at the pointwhose position. is to be determined, are received at the moment of phasecoincidence. It is arranged moreover that the emission of the signals Lcorresponding to the passing of the isophase line through the points ofunknown position situated betweentwo of these hyperbolae of coincidenceis so delayed' that this emission takes place upon the passing oftheisophaseline' through the first hyperbola ofZ coincidence that theisophase line encounters after' passing through the point' of" unknown'position.

ln this way'all the' signalsI L relative to the pointssitnated in thechannel comprised between two hyperbolae of coincidence are in a sensesorted' out andemitted at' the moment of the passage of the isophaseline through the hyperbola of coincidence that delirnitsy this channelin the direction of motion of the isophase line.

The screen will show, therefore', inwhichLchannelof the. network AB thepoint of unknown position is' located'. Position determination in thenetwork AB' is effected', therefore, by channels;

Now, if the line frequencyI of. the. television. tube. which receivesthe signals L is; given the value mst. it. would suffice, to. obtain thesecond' coordinate necessary for determining the position of the pointM5, to. delayf the; signal L. for a; period proportional tot` the timerlag: 11M correspondingy to'- the network: A'Bf and varying from zero toIt will be observed that while the determinationoipesition is effectedby channels in the. network it is effected in a continuous way in thenetwork ABL.

Hence, if the distance AB and the' distance AB" arev each divided intoalthousand graduations and it i'sassumed that. the exact coordinates of.themobilepoint are. 350 and 455. respectively along AB andA'B( and thenetwork AB isv divided. into 250.: channels, the. spot of thel signa-LLwill. bev positioned on the. television. tubescreen on the. esordi I2nate45.5. along A'B and on the coordinate 352' along AB (line. 88) v Byway of illustration, various systems utilized in accordance with theinventionI for effecting. a subjective andobective positiondetermination will now be described.. At. the same time there will bedescribed how a connection could' easily be conveniently establishedbetween the cont-'roll postwhere the objective position determinatioriseffected and any point of unknown position in the surveyed area, forexample between a control post and any one among several aircraft withinthis area.

Fig'. 10' illustrates a unitv of the transmitting systemsv adaptedtoeffect the positionrv determination.

At station A ai generator 4l produces pulses having the frequencyy p--q.These pulses vibrate a tuning fork S having a frequencyv p. The carriervwave FA emitted by the transmitter is modulated`v to the frequencies pand` The pulses p-q serve as the initial signals S.

Thev signal of frequency pA provides the synchronizing pulses nzSl forthe objectiveposition determination..

At station B the antenna 52 situated at point R. receivesv the wavevFA;modulated to the frequency p and to the frequencyf grs-11;y

The detector 53 detectsv the signal of frequency p.

Further, a detector 541 detects from. the wave FA a currentr offrequency pq which as in the case of the Fig. 5 drives at'nningzfork 9having afrequency q.

So long asi the isophase line passes-through R at such intervals thatthe.l time lag TR' remains constant i. e. so long as the' signals p andp-q are locked in frequency and in phase, the motor 44 remainsstationary. As soon as the time TR." changes'y the control device 57having two pentodes 49 and 50 (Fig. 9) provokes the rotation of themotor 44.. 'Ehe'. phase shifter 56 acts on the phase of the: current offrequency q and re-establishes the sit nation.

The carrier wave FB of the transmitter B is modulated at 58? to: thefrequency qt Thus the signal S of frequency p q and signal nS offrequency p are locked. in. frequency and inphase.

Fig.. l'l illustrates the devicel for' the objective positiondetermination and. ther selective connect-ionA to the point M of unknownposition.

rlhe amplifier? 1111 receives thel two modulated waves Fat andiFn..Filters 112 and E32 separate these two waves. Detectors 14 and 15 detectthe signals of frequencypand q. These'y frequencies` are transmitted tothe two selsyns 20 and 21 of the phasefmeter 59 which is. similar tothat of Fig.. 9 provided with a motor t44 and a control device 6'()which permits, the time. lag for each po sition to be read. on theindicator 60a. The passage of thev i'sophase. lineV provokes theemission of a; signal of frequency p-q. v This signal. is transformed atb into= a squared signal. of duration.

The signal of frequency pY is transformed at 60C by clipping andderivation, into pulses having a frequency p. These.- pulses are fed: tothe. grid 611' of a pentode 62- the' other` grid 63 of which. receives.the squared signals of duration;

Thus. only: thev pulse. of.. frequency p which immediately follows thepassage of the isophaee line. is' passed. by the- 13 This is eected bymeans AB and identical to that shown in Fig. 9. To this end, theindicator 64 could vdrive a `variable capacitor 63b forming part of thedelay line and having a capacity that varies in a continuous way as afunction of the time lag indicated by the indicator 64, its timeconstant varying in a continuous manner by an amount comprised betweenzero and The signal thereby obtained4V which constitutes theabove-mentioned signal L is transmitted to a transmitter 65 the carrierwave F1. of which it modulates.

Fig. 12 illustrates the system utilized at the `control post forreceiving the signal emitted by the transmitter 65 of Fig. 11.

The receiver 66 receives the modulated signal FL and detects the signalL which is applied to the Wenhelt grid 67 of a television tube 68.

Further, the signal FA is received at 69. The detectors 70 and 71respectively provide the signal S of frequency s=pq and the signal offrequency p. These signals are respectively transmitted to the line andfield synchronizers 72 and 73. The spot 74 which appears on the screen75 gives the position of the point M.

It is evident that a receiver similar to that of the control posts (Fig.12) could be placed at all points M of unknown position.

The signal L emitted from and received at the point M on board themobile object would be fed to the grid of the television tube and causeto appear on the screen thereof for instance a very bright spotindicating the position of the mobile object on the map` on whichhyperbolae of coincidence are drawn. l

The reception of the signals of position from the other mobile objectscould, for example, cause' to appear on the screen spots of lessintensity. lln this way an excellent anti-collision device is obtained.

However, such a device which is relatively cumbersome and costly couldnot replace, atv least on light aircraft, the simple position indicatorshereinbefore described.

SELECTIVE CONNECTIONS yApart from subjective and objective positiondetermination the systems in accordance vwith the invention enable theoperator of the post that el'ects the objective position determinationto put himself selectively in communication with any point having asuitable receiver within the area where the determination of position`is op erated.

To this end, the control post (Fig. l2) comprises on the screen 75 twocursors 76 and 77 perpendicular to one another. These cursors arerespectively mechanically connccted to the phase Shifters 78 and 79which receive the signals S and S' respectively pertaining to thenetwork AB and AB and impart thereto phaseshifts respectivelycorresponding to time lags 'r and -r pertaining to the point Whoseposition is defined on the screen 75 by the cursors 76 and 77. Thesignal S is transmitted from the detector 70. The signal S istransmitted from the detector 80a which detects the signals S' from thewave FA' received by the receiver 81. The transmitter 82 therefore emitstwo key signals C and C.

Each of the points whose positions are to be determined possesses twopentodes 83 and 84 (Fig. l1). One

grid of each of these pentodes receives respectively the passage signalof the network AB and AB formed respectively at 601 and 60d. The othercontrol grids of each of these same pentodes respectively receive thesignals C and C' emitted by the transmitter 82. When the two signalscoincide in their two pentodes 83 and 84, two relays close at 85 andunlock the receiver 86during a time `at least equal to the period ofsweeping T.

of`a delay line 63! (Fig. 1l) controlled by the indicator 64 pertainingto the network 14 Hence, only the aircraft selected by the oprator'ofthe" control post by means of the cursors 76 and 77 receives hismessages.

PULSE MODULATION It has been stated that the modulation of therespective carrier waves FA and FB by the signals of frequency p and qmay be effected by any of the known methods.

In the described example, it had been supposed that the modulationutilized was the sinusoidal modulation of the amplitude of the carrierwaves.

The particular features of the case in which pulse modulation isemployed will now be considered.

It is obvious that in this case there is no question of detecting phasecoincidences at any point in the surveyed area since the modulatingwaves of frequency p and q are replaced by pulses having thesefrequencies, two successive pulses being separated by silent intervals.Under these conditions, instead of detecting phase coincidences thesimultaneous reception at a point of two pulses will be detected, one ofthese pulses being emitted by transmitter D and the other by thetransmitter E (Fig. 13). This coincidence occurs along a certain numberof distinct hyperbolic lines. Position determination will be elected,therefore, by channels.

Furthermore, it should be noted that if the sinusoidal signals in thereceiver are transformed, in accordance with the normal practice ofclipping and derivation, into pulses, it will be found that thecoincidences of these kpulses thus obtained correspond to the moment atwhich the phase shift between the sinusoidal signals of frequency p andq is nil. In other terms, it is seen that the coincidence of the pulsesoccurs along position hyperbolae along which the phase shift is nil.

The coincidence hyperbola thus created moves therefore by bounds from Dtoward E if, as was supposed, p is slightly greater than q.

The same may be explained in the following way:

Assume that a line of coincidence (Fig. 13) forms at the instant tn onthe branch of the hyperbola intersecting the line that passes throughthe two transmitters D, E at a point Po, such that DPo=xu and PoE=dxo.Along this line of coincidence occurs the meeting of signal Do emittedat D at the instant and signal Fo emitted at E at the instant d xo wherec is the velocity of wave propagation.

A new signal E1 is emitted at E at the instant and a new signal B1 isemitted at B at the instant Similarly, any of the successiveV signals:emitted. at D, for example Dn emittedat the instant The line ofcoincidence, which. as already mentioned, very nearly coincides with theisophase line, is formed at intervals of'time ,zaini 2m on the branchesvof confocal hyperbolae having` focil D and' El intersecting DE at'pointsspaced apart a distance c 211g The line of coincidence of the signalsmoves thus from D toward E and coincides successively with the positionhyperbolae hu, hi lin that would correspond with the no phase shiftbetween the signals of frequency p. and q if the latter were constitutedby sinusoidall oscillations; The isophase line which coincides withthese position hyperbolae therefore traverses by bounds the spacecomprised between B and` E at a mean apparent velocity Beyond a point pmwhere PmE e there is no` longer coincidences between the correspondingysignals emitted at D and E because the signal DKm+i attains and passesthe point E before the instant when the signal Em+1 is emitted there. l

Of course, the same conditions of non ambiguity as that indicated in thecase when the signals of frequency p and q are formed by sinusoidaloscillations, must be satisfied: v

where T is the sweep period of the isophase line.

Advantageously, pulse transmitters are used having the same carrierfrequency for the two transmitters D and E. The high frequency chains ofthe two transmitters may be independent of eaclr other. The emissionfrequencies are stabilized in the usual way.

The carrier wave is modulated by stabilized pulse generators having afrequency in general not exceeding 1000 cycles'.

Eaclr signal emitted,l by the` transmitters D and E receives aparticular form. double pulse separated by a different interval of timefor each of the transmitters, say anV interval a for transmitter D and bfor transmitter E.

As in the aforementioned case of amplitude modulation, the frequencies pand q must be locked so that the sweep period T is constant.

In this case this locking may be achieved in the following manner:

A receiver termed monitor receiver is disposed in proximity to thetransmitter A. This receiver comprises a high frequency chain 77' tunedtothe carrier frequency common to the two transmitters E and D. Twofilters It may be, for instance, a j

69 respectively connected to the lters 78 and 79 simul- 78 and 79separatev the signals En and Dn. Each filter is essentially composed ofa pentode 80 whose grids 81 and 82 areconnected by a delay line 83 whosetime constant is set at value ak for the filter 78 and b for the filter79. Under these conditions, the tube 80 remains blocked so long as itstwo grids 81 and 82 do not receive simultaneously a pulse.. When thisoccurs, i. e. when the two grids are simultaneously polarizedrespectively by one of the components of the double pulse emitted by thecorresponding transmitter, these components being separated by a time aand b according to the transmitter that is equal to the time constant ofthe corresponding delay line, the tubei 80 emits and delivers a localsignal D and E.

The monitor receiver mayf be employed in dilferent ways for ensuringtheA stability of. the network i. e. for ensuringv that the coincidencesignal has the period T of the isophase line.

Thus, the signals D'v and E delivered by the filters 78 and' 79 may beapplied to an oscilloscope 84, the signal D being received there in theform of an upwardly directed spot and the signal E in the form of adownwardly directed spot. vThe time base of the oscilloscope S4 is equalto T. Thev operator. observes at a fixed point onf the screen thecoincidence of the points corresponding to a` signal A' and a signal B'.A multiplication of the sweep velocity by a whole number permits thiscoincidence to be: measured with great accuracy. If this coincidence no'longer occurs, the operator reestablishes it by means of a hand controlwhich enables him to remotecontrol the modulator from the transmitter Din suitably modifying thesphase of this oscillator.

A simple calculationv shows that if the frequencies p and q are definedwitht a relative accuracy E, the signals D- andzE that coincide atinstant, to, may be displaced by 22T at the start of the followingtravel, which represents a phase correction equal' to 42Tp=42(K-i1)radiansv of the oscillator.

Thel relative error E may be easily reduced to 10-1l or 10*5 and K is ofthe order of 100 to 1000. The phase `shift to effect is; then, of. a fewdegrees at the most. It

is achieved by adjusting the rotor of a variable capacitor inserted inone of the.` modulation chain circuits.

Alternatively, the stability of the network may be obtained by locking'the' frequencies p and` q as hereinbefore described.

Thus, each time ay mobile object possessing a detector capable of.detecting thecoincid'encey of the signals emitted by the transmitters D.and E is located onl a coincidence hyperbola, the coincidence signalemitted by this detector provides it with. an absolutely unambiguousindication of its position.

The unit for detecting the coincidence of the signals l emitted by thetransmitters D and E may, for example,

in the monitor receiver (.Fig. 14').

The filters.v 78V and 79 emit signals D' and E which are yapplied to thecoincidence detector itself (Fig. 16), the latter is. in essentialcomposed' of a pentode tube 87 that emits a coincidence signal when itstwo grids 88 and taneously receive: signals E and D'.

To determinev on what coincidence hyperbola the point of. unknownposition is located,; the time lag is measured in the same way as in thecase of amplitude modulation.

a through space asignalI HC inthe form of 'a double pulse comprise; twofilters 78. and. 79 similar to those included to, i. e. at the moment`when the simultaneous receptionv of the signals Du and Eo provokestherein the formation of the coincidence signal. If thereceiver islocated on the coincidence hyperbola n, it still receives the signal Hat the instant to, for the time to transmit the signal `H may beneglected. On the other hand, the coincidence signal is formed in thisreceiver atthe -moment of the reception of the signal Dn, i; e; at theinstant :url-nt. Now, t t

211g p y l Thus, between the signals H and-'C the 'receiver has receivedn signals emitted by A'. It suces, then, vto count these signals duringthis interval of time to` obtain the number of the curve upon which themobile object is located. v t

To this end, the mobile object comprises a pulse counter 93 (Fig. 17).This counter is set into operation by the signal H and stopped and thenre-set to zero by the signal C (signal emitted by the receiving point atthe moment when this point lies on a isophase line). This signal C atthe same time causes the registration of the numberof the coincidence`line on which the mobile object is located whatever be the point and thedirection in which the mobile object penetrates the area covered by thenetwork of coincidence hyperbolae.

lf the receiver is located betweenv two lines n-l and-n, it of coursedetects no coincidence for in this vcase the isophase line moves bybounds. It is to beV observed in this respect that the signal D11-1,reaches it a little later than the signal Enq, while the signalDntreaches it a little before the signal En. Thus, when the coincidenceline passes from the curve n-l to the curven, the receiver receives twosignals Dn-i and Dn consecutively and not separated by a signal E. Ifthe space comprised between the coincidence hyperbolae n1 and n istermed channel number n, the position of the mobile object could bedefined by a detector 95 -disclosing the succession of two signals Aunseparated by asignal E. By means f these signals this detector ofchannel 95 emits then, a signal Ch which in being fed to the counter 93of the signals D mentioned above, causes it to register the number n ofthe channel containing the receiver; (Fig. 17).

Several dilerent methods for producing this channel signal may beenvisaged. t

For instance, the following method may be employed. Pulses D and E fromthe `filters 78 and` 79 are regulated at equal amplitudes and are fed tothe grid of a thyratron. The connections are such that pulses D' give apositive voltage and pulses E'A arnegative voltage. Further, thepositive voltage fed by the pulsetD' is slightly less than thatnecessary for energizing the thyratron. When voltages correspondingrespectively to Athe pulses emitted at D and E are successively fed tothe grid of the thyratron, one cancels the other. At;the moment when apulse Dn-i is followed by a pulse Dn, without a pulse E interposedtherebetween, the twovoltages combine, then thyratron is energized and asignal Cn is emitted and fed to the counter instead ofthe signal C (Fig.17). This signal indicates that the mobilel object is` located betweenthe hyperbolae corresponding to .the Vcoincidence curves n-l and n, forthe detected instant'is the instant? when the isophase line coincideswith"lthe coincidence hyperbola n which is nearest the mobile object inthe direction of motion of the isophase liner kIn other terms, thecounter registers at each instant the number of the channel wherein thereceiving 'point;;,say-anaircraft, is

18 located, i. e. the number of the curve having the higher gure of thenumber of the two coincidence hyperbolae delimiting the channel inquestion. At the moment when the mobile object passes through ahyperbola, it is the number of the hyperbola that follows, in eitherdirection,

the number of the hyperbola previously registered that appears. Y

A coverage permitting a complete position determination is obviouslyconstiuted by two superposed networks ofthe above described type, thesenetworks utilizing either the` same carrierV wave `and dieringmodulating frequenciesy p and p1, q and q1 or diierent carrier Waves andthe same modulating frequencies. Two receivers tuned to the frequenciesof these two networks permanently ensure the registering of the twonumbers of the two channels, oneV in each channel which contain thepoint Whose `positionis `to be determined. In this Way the indication ofthe mes containing this point is obtained automatically and withoutambiquity.

y It is moveover possible to arrange that the transmitters D Vof the rstnetwork coincide with the transmitter D1 of the second network. Thecoverage then employs a single carrier frequency but the iive signalsD', E', H', H1 and Di are of different forms. The receiver of the pointwhose position is to be determined comprises tive filters.

With respect to objective position determination and selectiveconnections, there is no diierence between the system employing pulsemodulation and the system employing amplitude modulation by sinusoidaloscillation. I tis obvious, however, that objective positiondetermination is in this case carried out by channels along bothcoordinates instead of being carried out by channels along onecoordinate and continuously along the other as in the case of amplitudemodulation.

The invention is not limited to the details of construction describedand illustrated in the accompanying drawing which were given merely byway of example.

` Having now described my invention what l claim as new and desire tosecure by Letters Patent is:

4 l. In a system for determining the position of a re'- ceiving pointrelative to spaced transmitters; at least one pair'of spacedtransmitters for emitting a signal from each, the signals emitted by thetransmitters of each pair having different frequencies very close to oneanother and of such values lthat the velocity of propagation of thewaves inV kilometers per second divided by the sum of the frequencies incycles per second is greater than the distance in kilometers betweensaid two transmitters of ,v eachl said pair, whereby an isophase line iscreated which constitutes the locus of the points at which said twosignals are in phase and which moves from one of said trans- 4mitters tothe other, only one such line existing at any given instant, phasemeasuring means for detecting the passage of suc-h isophase line througha known point fixed in position, means for emitting an initial signalyfrom a point of known position, at the moment of such passage,additional phase measuring means for detecting the passage of saidisophase line through said receiving point, and time measuring means formeasuring the time Vlag between the reception of said initial signal atsaid receiving point and the passage `of said isophase line through saidreceiving point.

2. A system as claimed in claim l comprising means `for locking thefrequencies of said ltwo signals.

l3. A system as claimed in claim l including two of said pairs oftransmitters, the transmitters of one pair beging placed at the two endslof an axis passing through the c centre 'of the area wherein theposition determination is carried out and the transmitters of the otherpair being placed at the ends of another axis passing through theAcentre of said area, said two axes being substantially perpendicular toone another.

f4. In a system for determining the position of areceivingfpointrelative to spaced transmitters; at least one pair such away that the passage of said isophase'line through y a reference pointarbitrarily selected coincides with; the

'cedE transmitters fory e'n'iittifrrg'I assigns-1 freine.canti;r g av4carrier 'component 'aridamodultionf componen .A constituted by asinusoida ignaLfthe carrieco" ponen all) having differentfrequencies'and the modulation-signals emitted by the transmitters ofeach pair Shaving diterentv frequencies very close to one another and ofsuch valuesI that the velocity of propagation of the waves inkilorr'tet'ets per second divided by the sum ofthe frequencies inAcycles per second is greater than the distance in kilometers betweensaid two transmitters of each'said pair, 'whereby'v an isophase line iscreated which constitutes thelocus of the points at which said twosignals' arcrin phase and' which moves in a continuous way from one ofsaid transl' mitters to the other, only oneisuch line existing`at-jfan'yy given instant, phase measuring means for detecting thelpassage of schisophase line"thro`ugih a kow'n'epoint xed in position,means for emitt'ingfrom thisfpo'in't an' initial signal at the momentofsnch passage, additional phase measuring means fordetecting'the'passage'ofsaid isophase line through said receivingpoint,y and time measuring means for measuring the tmejlagbctween theVref ception of said initial signalat saidreceiving pointand the passage'of said isophas'eline through said receiving point; v

5. In a system for determining the positionof'a receiving point relativeto spaced transmitters; at leastonepair of spaced transmitters forvemitting from each'onea signal having a carrier component and an'iodulationrfcompol nent constituted by a sinusoidal signal, the'carrier' components all having different frequencies aridlth'emodulation signals emitted by the transmitters 'of eachpairfhavingYdifferent frequencies very near to one another 'and of such values thatthe velocity of propagation ofthe waves in kilometers per second dividedbyl the'l suin 'of the fre'- quencies in cycles per second is greaterthan the distance in kilometers between said two transmitt'ersof eachsaid pair, whereby an isophase line is created whichconstitutes thelocus or the points at which said two signals'are phase and which movesin a continuous wayjfrom one of said transmitters to the other, only onesuch liiieeitsting at any given instant, means fory emittingffromfonevof said transmitters an initial signal, means nfor regulating the phaseof at least one of said modulation signalsgin moment of the emission ofeach initial signal, phase measuring means forydetecting the passagedofsaid 4isophase line through said receiving point, andtimemeasuring meansfor measuring the time lag between theyreception of said initial signalat said receiving point andthe I passage of said isophase line throughsaid receivingpoint. 6. A system as claimed in claim 5-includingfmeanslfor modulating` with the initial signal the car- Iierwave; emitted by said transmitter that emits said initialsignal. A I 7.ln a system for determiningthe position `of-a receiving point relativeto spaced transmitters; at least one ;pair

of spaced transmitters including a first and a'secondtransmitter, meansat the first transmitter forjemittinga first carrier wave and amodulation initial signal havinga way from one transmitter to the other,phase measuring mea-nsllfordetecting: the passageiofv such isophase lineth ough alxedlpointssituated inI immediate proximity to oof?'saidtransmitters, means'for regulating the phase ofv'atil'east oneoffsaiczl modulation signals in such a Way that f t'lfiei:passage` oflsaid isophase-line through a reference pointlcoincide's .with themomentof the-emission of said initial@A signal, fphase:measuring meansfordetecting the passageofsaidisoplase line through said receiving pointandtiine.-measuring-meansfforf measuring the time lag, betweenithereceptionlofsaid initial signal at'said receiving point and the passageof said isophase line through said receiving point...

8. In a system for'vdetermining-the position of a receiving pointrelative to spacedftransmitters; at least one pairofi'spacedttransmitter-sier; emitting a signal from each, having-;acarrier; component andra; modulation component constituted-by; aisinusoidal signal, the, carrier-components allrhavingydiierentfrequenciesfand; the modulation signals emitted by the transmitters ofeach pair having different frequencies/very/,close to one, another andsuch that the velocity.' otipropagation. ofi the waves in kilometers persecond; dividedhyj the sum; ofi they frequencies in cyclesper-secondis-:greater thanf the.y distance in kilometers betweenjsaidtwo transmitters of saidpair, whereby an isophase ,line isv createdwhich constitutes the locus of the pointsgatf which said two signals arein phase and which movesin-'a continuous'way from one of saidtransmitters towthew'other, only :one such,` line existing at any giveninstance, phase measuring means for vdetecting the passage ofsuch`isophase line throughk a known point xed in position, means foremitting from this point an initial fsignalf'at'the moment of .suchpassage, phase measuring means for detecting the passage, of saidisophase line throughzsai'dir'eceiving point andV time measuring means.tlorinieasuring ithetime lag between the reception of said viinitial`fsign'al' ',atisaid receiving point and the passage of -said lisoplia'se'linet-hrough said receiving point said -means for detecting `fthepassage of the-isophase line comprising .means for'receiving said ftwomodulated carrierwaves, :means ffor ltering :each of-these carrierwaves, means fory detecting the modulation signal of each of thesewaves, l'a phasemeter comprising two perpendicular statorwindiingsiandz'arotor provided with a winding and a pointer,imens'i'forfeeding one-o'f said modulating signals to one offsaidstatoriwindings, means for shifting the phase of thissame'is'ignallSOfandtfeeding .it to the other of these :statorwindingg:means for feeding the other of said modulation signals to said rotorwinding, and means for iproducingan signal atthemoment-when-said'pointer passes :through the psitiomof nophase shift between thetwo saidisign'als.-

:9.z-In-a system forldetermining the position of a receivingpointrelativeito'spacedttransmitterm'at least one pair 'of.-'spacedttransmitters forllemittinga signal from cach,

first frequency which is the highest common suiza-multiplev`y- 460`{having-va ca'iercomponemiandamodulaton compnnem of a second and a thirdfrequency which arey dilerent and very close to one another and suchthat thevelocity of propagation of the waves in kilometers per-seconddivided by the sum of the frequenciesin cyc'lesfpersecondv,

is greater than the distance in kilometers between said twom" QVall-f'--constitutedtby,ia-sinusoidal-signal, the carrier componentstaillhavingtdiierent 'frequencies and llthe modulation sigfnlsemittedibyttheitransniitters offeach pair having dif- 'ferent'frequenciesiveryf'lseto one another and of such l-"that the'i'vlocityif-propagation of'the waves in kilometer/'smet'secondlf'r'iividedihy"thesum of frequencies iswgreate'r than thedistance in idftwoft'rfansmitters of said pair,

, leline/is create'd'which constitutes y A eipointsya"whichthesaid two.signals are fin phase and 4.which movel ,in .a. continuous way from onev of-said `ransrnrtter-s to :the other, enlyone such-line exist-.i-ngt-atianyfgiven-iinstanfphase measuring means for de- 'said thirdfrequency, meansfformodulating'withsaidg'tectiugtEthenpassagetofssuchrisophase.dinelthroughaknown ata-aser point fixed in position, means for emittingfrom'thispoint an'initial signal at the moment of such passage, additional phasemeasuring means'for detecting the passage of said isophase line throughsaidreceiving point and time measuring means for measuring the'time lagbetween the reception of said initial signal atsaid receiving point' andthe passage of said isophase line through said receiving point to saidtwo transmitters, said'means )for detecting the passage of the isophaseline comprising means for receiving said two modulatedlcarrier'wa`ves,"means for filtering each of these carrier waves, meansfor detecting the modulation signall of each of these'v carrier waves, aphasemeter comprising a rst selsyn` and a second selsyn the statorwindings of which are connectedphaseby phase, means for feeding to therotor of said first selsyn said first modulation signal and means forlockingj this rotor, means for feeding to the: rotor of said secondselsyn said second modulation signal, a pointerdriven by'said secondrotor and means for producing al signal at'the moment whensaid pointerpasses through the position of no phase shift rotors. i i

10. In a system for determining the position fof" a ire# ceiving pointrelative to spaced transmitters; at least one pair of spacedtransmitters for emittinga signal from each, having a carrier componentand a modulation component constituted by a sinusoidal SignaLthe carriercornponents all having different frequencies and the modulation signalsemitted by the transmitters of each pair having different frequenciesvery close to one another Aandof such values that the velocity ofpropagation of the Waves in kilometers per second divided by the sum rofi quencies in cycles per secondis greater than the distance inkilometers between said two transmitters of said pair, whereby anisophase line is created which constitutes the locus of the points atwhich saidt'wo signals are Iin'pha'se and which moves in a continuousway from one 'of said transmitters to the other,'only one such lineexisting a't any given instant, 'phase measuring meansfor`de`tect'inglthe passage of such isophase line through 'a known pointxed in position, means for emitting from this point an'initial signal atthe moment of such passage, additional phase measuring means fordetecting the passage ofsaid isophase line through said receiving pointand time measuring means for measuring the time lag between thereception of said initial signal atsaid-receiving point and the passageof said isophase line through said receiving point, said means formeasuring the time comprising a disc provided with a radial slit, meansfor driving 'thisv disc in rotation by means of said measuring meansutilizedfor detecting the passage of the isophase line; at least oneluminous tube placed behind said disc, 'means for causing the lightingof this tube at the moment of the "-reception of said initial signal,and a graduated disc placed in front of said disc and concentrictherewith covered with a iluorescent coating the remanence of whichduration substantially equal to that of the sweeping period of suchisophase line. l n i ll. In a system for determining the position of areceiving point relative to spaced transmitters; at least one pair ofspaced transmitters for emitting a signal from each having a carriercomponent and a modulation cornponent constituted by a sinusoidalsignal, the carrier componente all having different frequencies and themodulation signals emitted by the transmitters of eachy pair havingdifferent frequencies very close to one another and 4such that thevelocity of propagation of the waves in kilometers per second divided bythe sum of the frequencies in cycles per second is greater `than thedistance in kilometers between said two transmitters of said pair,whereby an isophase line is created whichconstitutes the locus of thepoints at which said two signals are in phase and which moves in acontinuous way from one of said Vtransmitters to the other, only onesuch jline existing at `any given-instant, phase measuring meansffrdetecting between thelsignalsfeeding said two the'v frethe passage ofsuch isophase line through a known point fixed in position, means foremitting from this point an initial signal at the moment of suchpassage, additional phase measuring means for detecting the passage ofsaid isophase line through said receiving point and time measuring meansfor measuring the time lag between the reception at this point of saidinitial signal at said receiving pointl and the passage of said isophaseline through said receiving point, said means for measuring said timelag comprising a first and a second selsyn the stator windings of whichare connected phase by phase, means for feeding said modulation signalsrespectively to the rotor windings of said two selsyns, a brush drivenby one of said rotors, two half-cylinders insulated one from the otherupon which said brush is adapted to rub in its rotation, two pentodes,one of the grids of each pentode being connected to one of thesehalf-cylinders, means for feeding said initial signal to the other gridof each of said pentodes, a motor arranged to drive the rotor of theother selsyn, meansfor feeding said motor through each of said pentodes,means for measuring the rotation of said motor, whereby said motor stopswhen the instant of the passage of said brush through the pointcorresponding to the nophase shift coincides with the instant of thereception of the initial signal.

l2. In a system for determining the position of a receiving pointrelative to spaced transmitters; a rst and a second pair oftransmitters, the transmitters ofeach pair being respectively positionedat the two ends of a straight line passing through the area within whichthe position determination is carried out and these straight linesintersecting, means for emitting from each transmitter a differentcarrier wave, in each pair means for emitting from each one of thetransmitters a modulation signal of sinus- -oidal form, the frequenciesof these modulation signals emitted by the transmitters of the same pairbeing differcnt and very near one another and such that the velocity ofpropagation of the waves in kilometers per second divided by the sum ofthe frequencies in cycles per second 'is greater than the distance inkilometers between said two transmitters of the pair, whereby is createdfor each pair of transmitters an isophase line that constitutes thelocus of the points at which said two modulation signals are in phaseand which moves in a continuous way from one of said transmitters to theother, only one such line existing at any given instant, in each of saidpairs, phase measuring means for detecting the passage of such isophaseline through a known point fixed in position, means for emitting fromthis point an initial signal at the moment of such passage, additionalphase measuring means for detecting the passage of said isophase linethrough said receiving point and time measuring means for measuring thetime lag between the reception of said initial signal at said receivingpoint and the passage of said isophase line through said receivingpoint, means for emitting a passage signal, at the moment of the passageof the isophase line pertaining to one of said pairs through saidreceiving point, means for emitting from one of said transmitters of oneof said pairs pulsed reference signals that have a :frequency equal to ntimes the frequency of the initial signal of said pair, whereby the areacomprised between the two transmitters of the considered pair is dividedinto .n channels by hyperbolae termed hyperbolae of coinci- -dence thatconstitute the locus of the points at which the jpassage of the isophaseline pertaining to this pair of 'transmitters and the` reception of saidreference signals -occur simultaneously, means for delaying said passage.signal pertaining to the same pair of transmitters until 'the momentwhen the isophase line the passage of which had caused this signalcoincides with the rst hyperbola -of coincidence that follows the pointwhose position is to 'be `determined in the direction of movement of theisogphase line, means for retransmitting said passage signal thusdelayed, means fordelaying the same signal for a tfllength of timeproportional to the time lag corresponding means for emitting adifferent carrier wave from each transmitter, in each pair oftransmitters means for emitting from a first transmitter a modulationsignal having a first frequency termed initial signal which is thehighest common sub-multiple of a second and a third frequency which aredifferent and very near to one another and such that the velocity ofwave propagation in kilometers per second divided by the sum of thefrequencies in cycles per second is greater than the distance inkilometers between said two transmitters, means at said firsttransmitter for obtaining by multiplication from said first frequency asignal having said second frequency, means for modulating said firstcarrier wave by said first and second frequencies, at said secondtransmitter means for emitting a second carrier wave, means forreceiving said modulated first carrier wave, means for detecting saidfirst frequency,

VVmeans for obtaining by multiplication from said first frequency saidthird frequency, means for modulating said second carrier wave with saidthird frequency, whereby an isophase line is created which constitutesthe locus of the points at which the signals having said second andthird frequency are in phase, this line moving in a continuous way fromone transmitter to the other, phase measuring means for detecting thepassage of such isophase line through a fixed point situated inimmediate proximity to one of said transmitters, means for regulatingthe phase of at least one of said modulation signals so that the passageof the isophase line through a reference point coincides with the momentof the emission of said initial signal,

phase measuring means for detecting at said receiving point the passageof said isophase line and means for measuring the time that elapsesbetween the reception at this point of said initial signal and thepassage of said isophase line through said receiving point, means foremitting a passage signal at the moment of the passage of the isophaseline relating to one of said pairs of transmitters at said receivingpoint, means for transforming said signal having said second frequencyinto pulses of the same frequency, whereby the area comprised betweenthe two transmitters is divided into n channels by hyperbolae ofcoincidence, which constitute the loci of the points at which thepassage of the isophase line and the formation of said pulses occursimultaneously, means for transforming this passage signal into asquared signal having a duration equal to the period of the signalhaving said second frequency, a tube having. several grids which isnormally blocked, means for unblocking this tube by applying said pulsesto one of the grids of this tube and said squared signals to the other,a delay line comprising a variable capacity and being adapted to delaysaid pulses by a length of time varying from 0 to the period of saidsignal having said second frequency relating to said first pair oftransmitters, means for varying the magnitude of said capacity by meansof said time lag measuring means relative to said second pair oftransmitters in proportion to the time lag, means for causing saidSignal transformed into pulses to pass through this delay line, meansfor retransmitting said delayed signal, a receiver comprising atelevision tube, means for receiving said retransmitted signal on thegrid of said television tube, means for applying the signal having saidsecond frequency relating to said first pair of transmitters to the linefrequency synchronizer of this tube, and means for applying said signalhaving said first frequency relating to said first pair of transmittersto the field frequency synchronizer of this tube.

20. A system as claimed in claim 19 further comprising two cursorsperpendicular to one another placed in front of the screen of thetelevision tube, means for receiving the initial signals pertaining tosaid first and said second pair of transmitters respectively, two delaylines controlled by these cursors for respectively delaying said twoinitial signals by a length of time respectively equal to the two timelags respectively relative to each of said tube pairs of transmittersand proper to the point whose position is defined on said televisionscreen by the intersection of said two cursors, means for emitting saidsignals thus delayed, at said receiving point two receiving channelsnormally blocked and the unblocking of which respectively necessitatessimultaneously the reception of the signal of the passage of theisophase line and the reception of said delayed signal both said signalsrelating to the same pair of transmitters, and a receiver that isunblocked by the unblocking of said channels.

References Cited in the le of this patent UNITED STATES PATENTS1,942,262 Shanklin Jan. 2, 1934 2,050,276 Chubb Aug. 11, 1936 2,141,282Southworth Dec. 27, 1938 2,419,525 Alford Apr. 29, 1947 2,436,376 BownFeb. 24, 1948 2,514,436 Alvarez July 11, 1950

